2004 Volvo Penta 5.0L OSi engines w/ duo props not getting on plane

serpico1

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I have a 2004 Rinker with twin 5.0L engines with ocean series duo props with SS props.
At the end of last season, after not using the boat for most of the season, I noticed that the engines ran fine at no wake speed as I drove out to open water. But, once I throttled up to WOT, I felt a slight vibration from the engines, I couldnt get above 3200 RPM and the boat would not get up on plane. There were no miss fires, back firing, or anything that indicated the engines were not getting enough fuel. Since it was the end of the season, I just waited for it to get pulled from the water for winterization to inspect the drives. Both drives and the bottom were covered with barnacles. So, i figured it was the drag from the barnacles causing the issue. barnacles were scraped and cleaned. I did notice a slight chip in one blade on one prop, but nothing major.

Now, here we are at the beginning of the new season and the same issue is happening. I checked the drives to make sure they were completely down. I have replaced the distributors and rotors ( the old ones did have corrosion on the contacts) But, that did not solve the problem.

The fuel is about a year and a half old. but it had been stabilized and additives such as seafoam added to it. again there is no miss firing that i can tell on the engines, no back fires or sputtering, nothing to indicate its starving for fuel. I checked the plugs they are not fouled, they are about 2 years old though.
Any Ideas?
Would one small chip in one blade of the prop cause both engines to not get over 3200 rpm and the vibration?
 

alldodge

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Is there any difference in RPM between motors when trying to get on plane?

One chip will not cause what your seeing

The fuel is old and seafoam is crap IMO and cannot make bad gas into good gas. If the gas is bad, there is no fixing, it has to be used up and new added or you just have more bad gas
 

serpico1

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Is there any difference in RPM between motors when trying to get on plane?

One chip will not cause what your seeing

The fuel is old and seafoam is crap IMO and cannot make bad gas into good gas. If the gas is bad, there is no fixing, it has to be used up and new added or you just have more bad gas
If it is the fuel, wouldnt that cause the engines to sputter and misfire?
they seem to run smooth as I travel around at no wake or slight wake speeds below planning speed.
 

Scott Danforth

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Engines will idle on crap fuel

Nothing you can add to fuel to make it last longer than 12 months from it's refinery date
 

serpico1

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ok
but I can drive the boat around without any issues at slow speeds under 3000 rpm
also, I had added about 30 gals of fresh fuel in Sept. there was about 15 gals of fuel left over from the previous year. So, not all the fuel is 1 1/2 yr old and as I said I do add in fuel stabilizers and other additives like stp fuel treatment or sea foam before the boat is decommissioned
 

Scott Danforth

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Adding good fuel to bad fuel makes more bad fuel
 

serpico1

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Ok,
But, im not quite sure its a fuel problem. I understand bad fuel will cause engine problems, as I had issues with stall fuel in small engines like my power washer, portable generator etc. but they usually just didnt start at all.

My boat starts and the engines run smooth and sound perfect during idle. They also do not give me any issues cruising around at 5 & 10 mph.

The problem only starts when I got to full throttle to go up on plane. They dont hesitate, misfire or backfire. They rev up to about 3000 - 3200 rpm and that is far as they go. I hear and feel a slight vibration coming from either the engines or the stern drives. The boat cannot get up on plane. If I had water in the fuel or the fuel was bad wouldn't it give me problems at all speeds and not just at wide open throttle?
 

alldodge

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Check fuel pressure, should be 50-60 psi on high side

If one motor was having problems the good one would not be able to produce enough power to get on plane. If one was ok and other had issues making power I would assume there would be a difference in rpm even slightly

Does each motor get fuel from a different pickup?

Does your boat have a motor sync option and if it does is it turned ON
 

serpico1

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ok,
I can select how where the engines pull fuel from. I can have each engine pull from separate tanks or both pull from either the port or starboard tank.

The boat has a sync meter at the helm. I did not look at it as I was going to WOT. But prior to that the throttles levers are even, and the meter says the engines are running in sync

I will have to check the fuel pressure on the high side.
although I have had fuel pump issues years ago. and usually when the high side cell is going bad or clogged, it starts to whine and at wot the engine had started to hesitate like it was running out of gas. not seeing those issues here. but I will put a gauge on it and see.
 

serpico1

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Aug 27, 2012
Messages
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Check fuel pressure, should be 50-60 psi on high side

If one motor was having problems the good one would not be able to produce enough power to get on plane. If one was ok and other had issues making power I would assume there would be a difference in rpm even slightly

Does each motor get fuel from a different pickup?

Does your boat have a motor sync option and if it does is it turned ON
Fuel pressure was check and it was 52 psi on both pumps on the high side at the fuel rail. If revved up both engines and it held with only a slight increase before returning to the 52 psi mark. Although, I did not check the pressure out on the water under a WOT load. Don't think it will change any.

I changed out both fuel filters. pour the gas into a clear glass container. The gas smelled and looked fresh, like it just came out the gas pump. there was no water or anything floating around.

I checked all the plugs and they all appear normal, no fouling or excessive burning.

So aside from all the suggestions regarding it being a fuel issue. Anything else I should look at before I just give in and bring it to the mechanic?
 
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